Homocysteine thiolactone and H 2 O 2 induce amino acid modifications and alter the fibrillation propensity of the Aβ 25-35 peptide.

Of the proteinaceous β-sheet-rich amyloid fibrillar structures, the Aβ 25-35 peptide, a component of the full-length Aβ involved in Alzheimer's disease, has similar toxicity to the parent peptide. In this study, the effects of homocysteine thiolactone (HCTL) and hydrogen peroxide (H 2 O 2 ) on the conformation and fibrillation propensity of the Aβ 25-35 peptide were investigated. Both HCTL and H 2 O 2 induced amino acid modifications along with alteration in aggregation propensity. Methionine (Met)-35 was oxidized by H 2 O 2 and aggregation was attenuated following the increased hydrophilicity of the peptide due to sulfoxide/sulfone formation. The HCTL-modified lysine (Lys-28) residue destabilizes the structure of the peptide, which leads to fibrillation. Our studies provide important information regarding the relationship between amino acid modifications and the amyloid fibrillation process.